The MicroETS system
reported elsewhere on this website, the new Micro ETS system
been installed on the Pont Croesor-Beddgelert Section of the railway
and a three month trial in the summer of 2012. This
by Roland Doyle
of Highrail Systems Ltd explains the principles of the system.
need for a Collision Avoidance System on a bi-directional single line
railway is obvious. At one time safety was achieved by putting a
policeman on duty on each single line section of a railway. The train
was not allowed to enter the single line section until the policeman
was aboard the locomotive. After a while, the policeman’s
truncheon became the symbol for the movement authority.
the ‘token’, it was placed on the hands of the driver, as the sole
authority for a train to occupy the section to which it
1888 the L&NWR invented an electrically worked instrument, the
Electric Train Staff (ETS). There was an ETS machine at either end of a
single line section, linked with copper cables. Each ETS machine has a
magazine to hold many tokens. When a token is removed from, or inserted
into an ETS machine, a change-over switch changes over. This switch has
two possible states, 'A' or 'B' known as the 'ETS polarity'. The system
is arranged so that when the line is clear (no token out), both
machines will have the same polarity. They will ether both be 'A' or
both be 'B', it doesn't matter which, so long as they are the same. On
the L&NWR system, the ETS machines at either end of a section
be in signal boxes staffed by signalmen.
When the signalman in
the local signal box wished to extract a token from his ETS machine, he
would arrange for the signalman in the remote signalbox to hold down a
key, which applied that ETS machine polarity to the transmission line.
This remote polarity was received at the local end, and if it was the
same as the local machine's polarity, the local machine would
unlock allowing a token to be released. The instant that token was
released, the polarity of the local ETS machine would invert causing it
to lock, since its polarity was now different from the remote machine.
This ensured that only one token could be removed from the system. When
was inserted to the ETS machine at the far end, the polarities would
then be the same again so that a token could be removed again. The
reason why the machines have several tokens is that subsequent trains
may travel in the same direction.
An advantage of ETS over Staff & Ticket working is the
to change the specific loop that trains pass without the need to move
the token by road. This is useful if one train is late and the other is
on time. The passing place can be changed so that the delay of one
train is not wholly passed on to the other.
been installed on the FfR in 1912, this system was later adapted by the
use of a remote-operator. On the FfR system, a small handle is wound on
a generator which applies an electrical signal to the transmission
line. Equipment at the remote end detects this signal and will apply
the remote ETS polarity to the line without the need for anyone there
to hold a key down. Thus the system can be operated by a single member
of the loco crew.
The MicroETS System
MicroETS system obtains the polarity of the remote ETS machine by using
secure double encrypted messages over the internet (or any other
medium which can support Internet Protocol). The Remote Operator on
the new system is currently a push-button switch. The remainder of the
equipment is kept locked away out of sight with a view to maintaining
the heritage feel of the system, similar to the original ETS system.
the ETS bench at each token station, there is a MicroETS
Outstation for each ETS machine. The outstation contains 4
microcontrollers, 3 'Channel Cards' for communications to the
outstation at the opposite end of the section and one event recorder to
log the processes associated with obtaining a token. The Event Recorder
even knows when the remote operator button was pressed.
MicroETS Management Server is a program currently running on a server
in Gloucestershire in a company that just rents out secure servers
which are attached to the high speed internet backbone in the UK. Each
time a token is removed or inserted into an ETS machine, the event data
is collected by the server in Gloucestershire. Another programme,
MicroETS Client, is used to read the data in the server and use it to
display a mimic diagram of the line, showing where a token is in or out
- see diagrams below.
If the token is out then
the direction of movement authority is shown by an arrow.
If you hover the cursor over the arrow, the time of token extraction
will be displayed in a tooltip.
The system has been developed by Highrail Systems Ltd, the principal
players being Ben Abbott (MicroETS Management Software), Roland Doyle
(MicroETS Outstation hardware & Software) and David Seelhoff
(DC-Uninterruptable Power Supply). Jim Comerford has been approved by
FfR Co to install the equipment. Jim has made very neat installations
at Pont Croesor & Beddgelert.
Safety and Security
Safety Critical Core parts are the Channel Cards. These are purpose
made for the MicroETS system. Since they are not PC based, they will
not just connect to any device sending a connection request. The
connection process is specific to the MicroETS protocol since Channel
Card 1 at Beddgelert will only ever need to connect to Channel 1 at
Pont Croesor, and so on. It's true that some clever would-be hacker
could 'spoof' a channel card (make his PC have similar credentials to a
channel card) But he will not know the password needed to complete the
connection process. In fact no one knows what that password is since it
changes every time.
Once connected, the channel cards
communicate with each other using encrypted communications. Even if a
would-be hacker could decrypt the messages, he's then faced with the
task of placing the correct key in his response message (the computer
engineering term for this key is a 'token' but in this case that just
confuses matters!). The key changes each time a message is sent.
Without the correct key, the message will be ignored. But there are 3
channels of inter-outstation communications, all with different
unrelated dynamic keys.
If the mains electricity supply fails at a token station, MicroETS has
battery backup which will keep the system running for at least 27
hours. However, the controller will know when the mains fails since he
is shown a power fail icon next to the token station on his mimic
part of the safety verification process, the system is being trialled
for 3 months. Shadow working is used whereby during the trial period,
the Guards operate the MicroETS system, keeping the ETS token out of
the sight of the loco crew, who operate the current 'live' staff
ticket system. The trial system is installed between Beddgelert
Pont Croesor. Many thanks to Steve Broomfield and Lyndon
who together with Roland Doyle have been showing the Guards how to
operate the system.
The FR Company, has asked us to look at the provision of operating
starting signals which would be set automatically by the removal of the
relevant MicroETS token, and cleared either by train departure or
reinserting the token into the machine it was obtained from.
This requirement has been allowed for by providing a
for the starting signal.
future development includes intermediate token machines (like the one
at Boston Lodge) and Long & Short Section Working (like the
Minffordd – Tanybwlch section which can be split into Minffordd – Rhiw
Goch and Rhiw Goch - Tanybwlch).
Update - October 2013
The trial system (Pont Croesor – Beddgelert) is currently
being soak tested
using Jim Comerford’s automatic testers which replicate the Remote
Operator Button push every 6 minutes or so. Later this year, we will
run two more trials with the equipment being operated by Jim’s
automatic testers. One trial will have an even number of tokens between
the two ETS machines – meaning ‘line clear”. This is the
reliability trial since the system should decide to release a token
each time. The system logs will show what was decided. The second trial
is the safety trial where there will be an odd number of tokens between
the two ETS machines meaning “line blocked”. In this case, the system
should decide not to release a token on every test cycle.
the Ff &WHR decide to adopt the system, then it will be
somewhere in the queue for funding behind Harbour Station redevelopment.
The assistance of
Roland Doyle in providing this article is gratefully acknowledged
Back to Home page
2012, updated 7th October 2013
by David Tidy